Process for producing methionine

Abstract

The present invention provides a process for producing methionine, which comprises steps of:hydrolyzing 5-[2-(methylthio)ethyl]imidazolidine-2,4-dione in the presence of a basic potassium compound in a non-stirred continuous first reaction tank, andheat-treating the reaction solution after hydrolysis in a second reaction tank. According to the process of the present invention, a methionine crystal with a higher bulk density can be produced.

Description

BACKGROUND OF THE INVENTION[0001]The present invention relates to a process for producing methionine by a hydrolysis reaction of 5-[(2-(methylthio)ethyl)]imidazolidine-2,4-dione [see the reaction scheme (1) shown below].[0002]Methionine is useful as an additive for animal feed.[0003]As an example of known processes for producing methionine, there is a process which comprises hydrolysis of 5-[(2-methylthio)ethyl]imidazolidine-2,4-dione under a basic condition using a basic potassium compound such as potassium carbonate or potassium hydrogen carbonate. According to this process, methionine can be separated and obtained as a crystal by introducing carbon dioxide into a reaction solution after hydrolysis to induce crystallization.[0004]An example of the above-described methionine producing process which comprises carrying out hydrolysis in a stirred continuous reaction tank is disclosed (e.g., JP-A 2007-99778).[0005]It is also known that a crystal of methionine is usually difficult to s...

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Benefits of technology

[0008]The present inventors have intensively studied and found that the amount of methionine dipeptide which is a by-product of hydrolysis in a reaction solution affects the bulk density of crystallized methionine, that is, when a larger amount of methionine dipeptide is contained in a reaction solution, crystallized methionine has a lower bulk density. Based on this finding, the present inventors have studied further. As a result, they have found that the amount of methionine dipeptide in a reaction solution can be reduced by carrying out hydrolysis in a non-stirred continuous reaction tank instead of a stirred continuous reaction tank, and the amount of methionine dipeptide can be further reduced by heat-treating the reaction solution to hydrolyze methionine dipeptide to methionine, so that the bulk density of crystallized methionine can be increased. Thus, the present invention has been completed.

[0013]When the hydrolysis is carried out in a non-stirred continuous reaction tank (first reaction tank) instead of a stirred continuous reaction tank, the hydrolysis proceeds while the starting material 5-[(2-(methylthio)ethyl)]imidazolidine-2,4-dione which is continuously added moves through the tubular reaction tank, so that the amounts of the starting material 5-[(2-(methylthio)ethyl)]imidazolidine-2,4-dione and the product methionine vary at portions of the reaction tank. In other words, at an upper portion of the reaction tank, the amount of the starting material 5-[(2-(methylthio)ethyl)]imidazolidine-2,4-dione is larger and the amount of the product methionine is smaller. In contrast, at a lower portion of the reaction tank, the amount of the starting material 5-[(2-(methylthio)ethyl)]imidazolidine-2,4-dione is smaller and the amount of the product methionine is larger. Therefore, in the case of using a non-stirred continuous reaction tank, the amount of the by-product methionine dipeptide is reduced because one of the starting material 5-[(2-(methylthio)ethyl)]imidazolidine-2,4-dione and the product methionine is always smaller in amount than the other, unlike in the case of using a stirred continuous reaction tank wherein both compounds are always present in constant amounts.

[0014]After completion of the hydrolysis, a reaction solution containing a reduced amount of methionine dipeptide as described above is subjected to heating treatment, and thereby, methionine dipeptide is converted into methionine through hydrolysis and thus the final amount of methionine dipeptide produced as a by-product is further reduced.

Problems solved by technology

It is also known that a crystal of methionine is usually difficult to stabilize because it is a flake crystal, and therefore a flocculant is required for crystallization.

When hydrolysis is carried out in a stirred continuous reaction tank as described above, the resultant methionine crystal has a low bulk density, resulting in a high equipment cost.

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